Preliminary experiments suggest a hypothesis for cochlear hair cell function that includes not only transduction but also an active role in cochlear mechanics. We propose to study cochlear electromechanical processes using several existing in vivo and in vitro techniques. We plan to study the effects of altering both cochlear potentials and ionic concentrations on several measures of cochlear response. These include the measurement of mechanical nonlinearities, which give rise to distortion of the acoustic signal measured near the tympanic membrane, as well as the response properties of auditory-nerve fibers to single-tone and two-tone stimuli. We propose to alter cochlear efferents or by injecting electrical current into the cochlea. We expect to find correlations between the more direct mechanical measurement (distortion in the ear canal) and the neural measurements. In order to make more direct measurements of hair cell electromechanical properties we propose a complementary series of in vitro experiments using existing organ of Corti tissue culture techniques as a starting point. These experiments will enable us to substantiate hair cell properties suggested by our past and future in vivo experiments.